Atomic layer deposition (ALD) is conventionally carried out in a reaction chamber under vacuum conditions. One or more substrates are first loaded into the reaction chamber and then vacuum is provided or sucked into the reaction chamber and the reaction space inside the reaction chamber is heated to process temperature. The atomic layer deposition is then carried out by supplying and pulsing first and second gaseous precursors into the reaction chamber alternatingly and repeatedly for providing a coating layer with desired thickness on the surface of the substrate. A full ALD cycle, in which the first and second precursor are supplied into the reaction chamber comprises: supplying a pulse of first precursor into the reaction chamber, purging the first precursor from the reaction chamber, supplying a pulse of second precursor into the reaction chamber and purging the second precursor from the reaction chamber. Purging precursors may comprise discharging the precursor material from the reaction chamber, supplying purge gas, such as nitrogen, into the reaction chamber and discharging the purge gas. When desired number of ALD cycles and thus a desired coating layer thickness is reached, the vacuum in the reaction chamber is released and the substrates are unloaded from the reaction chamber. Then the same process is repeated for the next substrates.
An alternative way of providing coating layers on a substrate with ALD is using movable nozzle head which comprise at least one first precursor nozzle for supplying first precursor on the surface of the substrate, at least one second precursor nozzle for supplying second precursor on the surface of the substrate and at least one discharge channel for discharging the precursors from the surface of the substrate. The nozzle head comprises on output face to which the precursor nozzles and the discharge channels are provided. The nozzle head is arranged over a surface of the substrate to be coated and moved in reciprocating or similar manner over the surface in relation to the substrate. The relative movement of the substrate and the nozzle head may be carried out by moving the substrate or the nozzle head over alternatively moving both the substrate and the nozzle head in relation to each other. The precursors are supplied continuously and uninterruptedly from the precursor nozzles and also discharged to discharge channels. The relative movement and continuous supply of the precursors subjects the surface of the substrate alternatively and repeatedly to the first and second precursors and grows coating layers on the surface of the substrate.
The disadvantage of the prior art ALD coating methods and apparatuses is that forming coatings having different coating layers, meaning nanolaminate coatings, is difficult. The methods and apparatuses are designed to for only coating layers having one type of coating layer. Forming nanolaminates requires disrupting the coating process and adjusting the apparatus in order to form a different coating layer. When the coating is formed in a reaction chamber, the used starting materials have to be changed and the supply of the precursors have to be disrupted. If nanolaminates are produced with prior art nozzle heads without disrupting coating process, the nozzle head have to have extremely large number of precursor nozzles, as the nanolaminate structure is defined by the precursor nozzles of the nozzle head. This means that the nozzle head have to have suitable number of different precursor nozzles corresponding the desired nanolaminate structure. Furthermore, the conventional pulsing of the starting materials into the reaction chamber is slow as the whole reaction chamber has to be exhausted and purged between the different precursor pulses. However, when nozzle head is used, the precursors are supplied continuously from the precursor nozzles and nozzle head and the substrate are moved relative to each other. Therefore, when the coating comprises different coating layers, the supply of the precursors and the movement of the nozzle head have to be disrupted and the precursors changed so that the new coating layer may be formed using different precursors. Alternative, the different coating layers are formed in different reaction chambers or with different nozzle heads. This makes the process complicated and modifications of different coating layers in the coating difficult and complicated.